The Lake Merritt Rock Garden

Thirteen individual gardens, each supported by different member clubs or volunteers, make up the GLM. These include an enclosed Bonsai and Suiseki garden featuring an extensive collection of trees and stones, a Japanese garden and Oakland-Fukuoka sister city garden, a pollinator garden focused on native bees and butterflies, the Mediterranean, sensory and palmetum gardens, as well as areas that grow vireya rhododendrons, succulents, dahlias, and roses. There is also a large community garden, a collaboration section with Merritt College, and many smaller groups specializing in particular plants.
The Board encouraged our rock garden group to create a demonstration rock garden at the GLM. The site is at a central point in the garden between the community gardens, pollinator gardens, bonsai, and the Fukuoka sister city gardens. The site is shaped like a half pear around 50 feet (15 m) long and 30 feet (9 m) across. It is a nice space for a trough garden. It has full sun and has been connected to water by Public Works. Given its location surrounded by paths, many visitors can view the rock garden up close.
Rock gardening in the Bay Area
The San Francisco Bay Area has a range of microclimates from the cool and foggy coast, to an intermediate zone around the Bay, to the hot and dry inland regions. Oakland is in the intermediate zone. It rarely freezes and on occasion may go above 90°F (32°C). In general, the summers are warm and dry, and the winters have rain, with less precipitation during droughts. With climate change, it is likely that our region becomes warmer and drier in future decades.
Most alpines can grow in the cooler regions of the Bay Area, and a few can grow in the heat. New Zealand alpines such as Raoulia do particularly well in the area, given regular watering. Plants that require dry winters or freezing cold while dormant are more challenging.
Design and Planning
The basic design is a perimeter of 12 large troughs on a gravel bed, with a crevice garden in the center. Much inspiration was drawn from the trough garden at the University of British Columbia, with its elegant set of troughs over a gravel bed.
In creating the crevice garden, we studied many pictures on the internet. Locally, the Regional Parks Botanical Garden (sometimes called the Tilden) in Berkeley has a crevice garden focusing on California native plants on a much larger scale (See the article in the Summer 2021 issue of the Quarterly). We studied Zdeněk Zvolánek’s great book The Crevice Garden and its Plants. His book is invaluable and has a lot of technical advice on soil composition and how to construct layers.
The most natural-looking crevice gardens seemed to have a uniform stone color, a general alignment of the slabs, parallel ridges and curves of stones, few jagged points or corners, limited gaps, and thin rocks wedged among thicker slabs. All of these elements together give the illusion of a solid rock mass. We used these concepts in building our bed.
Constructing the garden
As part of a public garden, permission for volunteers to garden on a public site was obtained through Oakland’s Adopt-a-Spot Program. We provided a plan to the Oakland Department of Public Works (DPW) section overseeing the Gardens for approval and coordination with City staff. A funding request was submitted to the GLM Friends Board which provided matching funds for the project.
In February 2020, we started building the 12 troughs. We wanted to make large troughs and took into consideration the weight for moving them later. After researching hypertufa formulas to balance weight and strengths, we settled on a formula with 30% Portland cement, 40% perlite, and 30% coconut coir. Coconut coir was used instead of the traditional peat moss for both environmental reasons and strength. A local trough maker and Western Chapter member, the late Shigeo Kubota, had noticed that coconut coir had long fibers that would reinforce the hypertufa, and so we added even more coconut fibers in the mix.
The troughs were made in four shapes: straight and tapered rectangles, tapered squares, and rounds. For the box shapes, we created molds out of plywood and for the rounds we used a 64-gallon circular tub. The hypertufa was reinforced internally with hard wire mesh, chicken wire, screens, and various concrete reinforcement fibers to make the troughs as strong as possible. Empty, the troughs weigh roughly 125-275 pounds (57-125 kg) each. After a major delay from COVID closing access to the gardens for a few months, the troughs were completed by October 2020.
Clearing the ground began in March 2020, but was interrupted by the COVID pandemic. The work resumed in December and was completed on weekends by January 2021. Groundwork included clearing the plants, leveling the ground, and excavating an area for the crevice garden. Landscape fabric was laid over the entire garden site in conjunction with the irrigation lines placed by the City. Cinder block platforms were placed where the troughs were to be located.
The major work was conducted over a three-week period in late January to early February 2021. Bill Castellon, a local landscaper and Japanese garden specialist, led a volunteer crew to move the heavy troughs from our production area to the garden site. His large tripod, pulley, and a heavy-duty cart made the job much easier. With the troughs in place, drip tubing was installed as we filled the troughs with soil and amendments, and all 12 troughs, demonstrating various trough gardening styles, were planted in February 2021.
The stone and materials were delivered, and a group of volunteers laid out the crevice garden. The crevice garden was built layer by layer. The crevice garden was built on a slight mound rather than flat ground which allowed us to get greater height in the middle. The bottom layer was made of ledge stone and rubble. The second and third layers used more vertical slabs.
Once the troughs and crevice garden were mostly completed, gravel was brought in to cover the main bed. The Department of Public Works advised us to slope the gravel bed down to the path with a small depression around the perimeter to decrease gravel from spreading out to the surrounding pathways. This required a little more digging and groundwork. Once construction was finished, Ray Deutsch and Nancy Havassy began to plant into the crevice garden mainly using plants from the propagation collection and a few from private collections.
Planting Conditions
We designed the soil mixes and watering regimen to match the local conditions, the type of garden, and plant needs. There was heated debate on how lean and dry the soil mixtures should be. The main disagreement was between those who grow alpines in wetter conditions and those who use much drier conditions. Compromises were made and we were able to move forward with the project.
The soil mix is a little on the rich side to retain moisture. The mix uses a soil mix from a local landscape company as well as perlite and pumice to provide drainage. The general proportions are about 50% organic and 50% inorganic. While there was a preference for a much leaner mix, the inconsistency of watering was a driving concern. A couple of times during COVID in 2020, water lines in the Gardens were damaged and water was cut off in the gardens. Many of our plants would not be able to handle three to four days of dry heat. There are a few hidden catch basins in the troughs so that they can hold water in extreme heat if needed. Currently, the plants in the rock garden are hand watered every other day in the summer. A drip irrigation system was installed but the timers are not connected at this point.
The soil depth in the troughs is around 9 to 12 inches (23 – 30 cm) to give the plants some root space. In the crevice garden, the soil runs around 12 inches (30 cm) below ground level and the rock formation reaches 6 to 24 inches (15-61 cm) above ground level. From the top to the bottom, the soil depth in the crevices is between 18-24 inches (46-61 cm) depending on the location. There is a layer of landscape fabric under the crevice garden to prevent weeds and gophers from entering the crevice garden from below.
Descriptions of the troughs
The first trough is a miniature landscape, sort of a mountain glade. This is similar to a style chapter member Wally Wood used at the San Francisco Botanical Garden many years ago. The front mat plants, representing grass in a mountain glade, include Raoulia lutescens, R. australis, R. hookeri, and R. apice-nigra. Floral color comes from Dianthus ‘Blue Hill’, Erigeron vagus, Centaurium scilloides, and Erigeron leiomerus. The planting has Juniperis communis 'Compressa' as trees behind the meadow with triangular flagstone pieces used to represent a mountain range in the background.
Another trough features vegetable sheep, the cushion forms of Raoulia, not to be confused with the many flat-growing Raoulia (scab weeds). The closest plant we have to the vegetable sheep is the hybrid Raoulia x loganii. The initial planting used black rock for contrast with the silver cushions. This may have become too warm and the initial plants died off. We recently replanted with a lighter stone and a new set of Raoulia x loganii. The new rock also features colorful lichen which we will try to maintain. While the trough is still a little warm in the sun, hopefully this group will be able to make it.
Acantholimon litvinovii is paired with red stones and amendments in another trough. These plants have thrived in the first six months, filling out into tight spiny mounds. The red stones were provided from suiseki (a Japanese tradition of collecting small interestingly shaped rocks) collectors Janet Roth and Steve Nelson. They create a nice contrast to the silver cushions.
The trough crevice garden shows how to use the crevice style in a container. By aligning the rocks and creating parallel ridges, the slabs create the sense of a solid mass. It uses the same stone as the larger crevice garden. Currently, it has a Leontopodium alpinum, Campanula bellidioides, Dianthus arpadianus var. pumila, Raoulia apice-nigra and various succulents.
Another trough shows a mosaic style of alpine plants including various Raoulia and other mat plants. These fill in and change over time. This planting includes Raoulia australis, R. haastii, R. hookeri, R. lutescens, Scleranthus uniflorus, Dianthus ‘Blue Hills’, Sempervivum arachnoideum ‘Minor’. At this time, the Raoulia australis is a little too aggressive and will get swapped out with other plants.
Local rock planted to suggest a winding river bed within a canyon defines another of the troughs. A number of cushion and mat plants are tucked in between the rocks, including Scleranthus uniflorus, Arenaria alfacarensis, Silene acaulis ‘Frances’, and Arenaria ‘Wallowa Mountains’. These will grow over time and blend in as part of the rock formations.
The Japanese garden trough reflects the Japanese gardening influence at the GLM. Historically, there was a strong involvement of local Japanese gardeners in the GLM as can be seen in the Oakland-Fukuoka sister city garden section, Japanese garden, and the Bonsai and Suiseki collections of the larger Gardens. This trough imitates the island style of Japanese garden, using the green Raoulia lutescens as moss. The island is surrounded by a sea of white dolomite gravel.
The flat green trough uses Raoulia lutescens in a minimalist style featuring just a single plant species. Over time, the trough will have a flat top of green flowing over the edges.
We have a trough garden designed around a large stump. The stump will age and decay over time, and contrast with Papaver alpinum, Linaria alpina, Thymus camphoratus, Aquilegia chrysantha, and other plants.
The trough featuring mostly European alpines is currently dominated by Leontopodium alpinum, but also includes Gentiana acaulis, Gentiana verna, Saxifraga paniculata, Saxifraga cochlearis 'Minor', Salvia caespitosa, and several Edraianthus.
A trough of North American alpines includes Eriogonum kennedyi, Aquilegia jonesii, Erigeron leiomeris, and other plants. In time, the Eriogonum kennedyi will spread over the trough.
The final trough is in transition. Originally planted with five large Gypsophila aretioides to form a dense green formation, these were removed after one of the plants was stolen. We couldn’t stand the idea of someone coming back and taking the rest. Currently, the trough has a mix of annual alpines and Meconopsis horridula. This will likely be replanted in the winter.
The Crevice Garden
The crevice garden is around 12 feet (3.7 m) long and 9 feet (2.7m) across. It uses about 8 tons of stone. It has three layers: a base uses a mix of ledge stone and local rock (rubble), vertical slabs, and finally shattered pieces of flagstone and gravel scattered over the top to help fill in gaps.
Volunteer Kyle Milligan and others helped place the rocks to create a natural look. The rocks are packed so tight that the mound can hold weight from above. A mix of soil, sand, and pumice was usedto fill under and in between the slabs. The soil was placed under and between the layers, and prodded and hosed down into the gaps in the slabs. We tried to avoid any air pockets.
Ray Deutsch and Nancy Havassy planted in a wide variety of small rock garden and alpine plants on the crevice mound. Plants that grow too large are pulled and replaced.
In a related project, we planted meconopsis in another section of the gardens. We planted mainly Meconopsis baileyi, M. ‘Lingholm’, and M. grandis, with a few other varieties. The plants took hold under some redwoods where we have automatic watering and a thick mulch. Over the next several months, we will be expanding this patch and enriching the soil. The plants will go dormant from December to February. We look forward to next year’s bloom in April and May as the plants will have had sufficient time to establish.
The future
The garden will mature over the next several years. In the meantime, we will continue to add and remove plants, and to provide ongoing care for both the garden and collection. With the collection and the new demonstration garden in place, we will establish the Gardens at Lake Merritt as the new base for the Western Chapter in the next several years. The rock garden demonstrates what can be done with trough and crevice gardening. The propagation collection holds many alpine and rock garden plants that do well in the Bay Area. There will be opportunities for workshops on rock gardening, trough making, and plant propagation as we come out of the pandemic. And as the garden matures and becomes established, we welcome our fellow rock gardeners and NARGS members to visit our garden and collection!

We would like to acknowledge the many people who helped build the garden and contributed funds or materials.
The project was organized by John Tsutakawa and Kiamara Ludwig. Thank you to Tora Rocha, FGLM co-president who provided major support, coordination, and advice on setting up the garden. Thank you to DPW supervisor Lydia Swann and DPW staff Juan Cana-Cruz, Bali Kashmiri, and Jay Tubbs for their assistance in clearing the ground, laying irrigation lines, moving materials, and selecting the site.
Thank you to our core group of regular volunteers and friends for maintaining/moving the propagation collection and working on the project which includes Ray Deutsch, Nancy Havassy, Pat Clinton, Alice Eastman, Emi Tsutakawa, Dottie Lovett, Ray Dyer, Troy Smith, Nancy Chu, Owen Smith, Diane Glaub, and Kerry Barrs. Special thanks to Bill Castellon for moving the troughs, John Keefer on the irrigation, John Kirkmire on the video, and Kyle Milligan and Kevin Takakuwa for the long hours on the crevice garden. Many volunteers helped with the troughs, the groundwork, and the crevice garden. These include Tomas Zillman, Danny Morton, Barry Luck, Becky Babb, Tu Le, Mary Mortimer, Tracy Johnston, Leslie Elledge, Woody Miller, and Brandon Casbeer.
Thank you to the Friends of the Gardens at Lake Meritt, John Tsutakawa, and David Deutsch for financial support and to Janet Roth, Steve Nelson, Kiamara Ludwig, Haru Kubota, Pat Clinton, and Kevin Takakuwa for their material contributions to the project.
If you want to keep up with activities at the garden, follow the Western Chapter’s Instagram: